The present invention relates to a fuel tank comprising an vessel for containing fuel and a gas evacuation system.
In order to fill a fuel tank without causing fuel to back up in the filler tube, it is known that the gas contained in the tank must be allowed to escape as the level of liquid in the tank rises.
It is also known that the motion of a vehicle subjects its fuel tank to shaking that causes fuel vapor to appear over the liquid fuel, which fuel vapor must be evacuated since otherwise the tank can be subjected to dangerous rises in pressure.
However, it will be understood that evacuating fuel vapor in this way must take place without any liquid fuel being able to escape from the tank together with the vapor.
To this end, it is known to provide a tank with one or more gas evacuation ducts connected to respective devices (which are generally check valves) having various functions including the function of allowing gases to pass while preventing liquid fuel from passing. This is referred to as the separate liquid from vapor (SLV) function.
In addition, if the configuration of the tank makes it possible, those devices can perform additional functions such as, for example, preventing the tank being overfilled so that there always exists a bag of gas above the level of the liquid so as to preserve capacity for the volume of the fuel to expand or so as to prevent liquid fuel from flowing through the evacuation ducts in the event of the vehicle rolling over. This function is also known as the roll-over valve (ROV) function.
As a result, the structure of known devices is very complex, which gives rise to problems of cost and reliability, since the moving portions of said devices can jam in the open or in the closed position, which in either case prevents them from performing their functions.
There therefore exists a need for a device for evacuating gases that is reliable and cheap and that has no moving parts.
The present invention seeks to satisfy this requirement.
The present invention provides a fuel tank comprising a vessel for containing fuel and a gas evacuation system contained in the vessel, said system having a passage putting the inside of the vessel into communication with the outside of the vessel and a membrane closing said passage, the membrane being suitable for allowing air and fuel vapor to pass therethrough while preventing liquid fuel from passing therethrough, wherein the membrane is situated inside the vessel and extends over the major portion of the top wall of the vessel.
In a particular embodiment of the invention, the membrane includes at least one layer of a porous fluorine-containing polymer of open-cell structure.
Such a membrane can be made of a material known under the trademark GORETEX.
To implement the invention, it is also possible to use the xe2x80x9cPERMEONxe2x80x9d membrane from EGC Corporation, Houston, Tex., USA.
The membrane of the invention can be placed at any point of the tank situated above the liquid level, so as to remain permanently in communication with the volume of gas enclosed in the vessel, thereby enabling said volume of gas to remain substantially at atmospheric pressure.
The membrane of the invention has the advantage that in addition to performing the SLV function, it replaces the ROV device which prevents liquid fuel from escaping via the fuel vapor evacuation duct in the event of the vehicle rolling over.
Thus, the membrane of the invention performs both the SLV and the ROV functions.
In a particular embodiment, the passage is made by an opening formed through the top wall of the vessel, the membrane extending across said opening, the fuel tank also having a closure member covering the membrane and closing the opening in leakproof manner, which closure member is fitted with a coupling endpiece for coupling to an evacuation duct to put the duct into communication with a space lying between the membrane and the closure member.
In this embodiment, the closure member can include a support grid extending substantially parallel to the membrane and supplying it with backing in the event of force being exerted by the liquid fuel contained in the vessel, e.g. while the vehicle is in motion or if the vehicle rolls over following an accident.
In a preferred embodiment, the vessel is obtained by bonding together two vessel portions obtained by injection molding, the bonding being performed by heat-sealing or adhesive.
The invention also provides a device comprising a fuel tank as described above and fuel vapor recovery means connected to the passage closed by the membrane and putting the inside of the vessel into communication with the outside of the vessel.